// looking up users, fetching additional attributes etc.
type Provider interface {
	LoginWithUser(username, password string) error
	LoginWithClientID(clientID, clientSecret string) error
	LookupUser(userid string) (User, error)

// returned error is of type [UnknownUserError].
func Lookup(username string) (*User, error) {
	if u, err := Current(); err == nil && u.Username == username {
		return u, err
	}
	return lookupUser(username)
}

// LookupId looks up a user by userid. If the user cannot be found, the
// returned error is of type [UnknownUserIdError].
func LookupId(uid string) (*User, error) {

package user

import (
	"fmt"
	"runtime"
	"strconv"
	"strings"
	"syscall"
	"unsafe"
)

func current() (*User, error) {
	return lookupUnixUid(syscall.Getuid())
}

func lookupUser(username string) (*User, error) {
	var pwd _C_struct_passwd
	var found bool
	nameC := make([]byte, len(username)+1)
	copy(nameC, username)

	err := retryWithBuffer(userBuffer, func(buf []byte) syscall.Errno {